Fully Conjugated Donor-Acceptor Covalent Organic Frameworks for Photocatalytic Oxidative Amine Coupling and Thioamide Cyclization

Covalent organic frameworks (COFs) are promising candidates as heterogeneous photocatalysts because of their porosity and tunable light absorption. The photostability and charge separation of COFs are highly important to improve the efficiency of photocatalytic transformation. In this work, a fully conjugated donor-acceptor COF is constructed with a benzothiadiazole unit, which exhibits high stability and enhanced charge separation. The prepared COF can efficaciously produce superoxide radical anions under air and visible light, which mediate the photocatalytic oxidative amine coupling and cyclization of thioamide to 1,2,4-thiadiazole in moderate to high yield and high recyclability (18 examples). This study demonstrates the great capacity of fully conjugated COFs with a D-A structure for light-driven organic synthesis.